1. Field of the Invention
The present invention relates to image reading apparatuses, and more particularly, to an image reading apparatus having a plurality of light sources with different color tones from each other.
2. Description of the Related Art
White-color light emitted from a light source in an image reading apparatus is implemented by adding a plurality of light components. More specifically, a blue or ultraviolet electromagnetic wave (hereinafter simply called “light”) emitted from a predetermined LED light source is incident on a phosphor member to be converted to light having other wavelengths, such as yellow light, and is added to other light components to obtain white-color light. Since the light-emission efficiency of the phosphor member varies according to the wavelength of light emitted from the light source, a slight change at wavelength produces a corresponding change in the amount of light emitted from the phosphor member. This latter amount also varies in accordance with the amount of phosphors included in the phosphor member. As a result, the obtained color tone differs from one white-color LED to another. (By “color tone” is meant color quality, such as a color combination, color shading, and color strength; or color tint, such as, for example, a tone difference in an HSV color space.) More precisely, common color tones are pure-white light, a white light with a yellowish tone, and a white light with a bluish tone. Since such differences in color tone can be visually recognized, they cannot be ignored.
When a color image is read without taking color-tone variations of light sources into consideration, a color-tone variation occurs in the resulting image data (at least as compared with data obtained using a different light source). In addition, since a color-tone variation occurs also among light-source modules serving as illumination means, color-reading quality deteriorates.